Astronomy - June 2015

ASTRONEWS

Mercury

Earth’s

Moon

Vesta

Dawn spacecraft

Ven

us

Earth

Mars

Ceres

ASTEROID^ BELT

Vesta

Jupiter

Thin,

dusty

outer

crust

Water

ice

layerRocky inner

core

Ceres

WWW.ASTRONOMY.COM 13

Jupiter moons captured in rare triple transit

There was no dramatic entry. No high-risk maneuvers or

nail-biting rocket firing. If NASA’s Dawn spacecraft missed

on its slow crawl into orbit around the dwarf planet Ceres

early on March 6, engineers would have just tweaked the

weak thrust of the ion engines and tried again. Instead,

mission managers say the real drama will be the science

unveiled as NASA chronicles the history of the largest

unexplored body in the inner solar system.

“Since its discovery in 1801, Ceres was known as a

planet, then an asteroid, and later a dwarf planet,” said

Dawn Chief Engineer Marc Rayman on the 6th. “Now,

after a journey of 3.1 billion miles (4.9 billion kilometers)

and 7.5 years, Dawn calls Ceres home.”

Ceres — the largest member of the main asteroid belt

— is Dawn’s second target. The spacecraft spent 14

months exploring Vesta, the second-largest asteroid.

Together, the pair make up 40 percent of the belt’s mass.

The rest of the belt represents a multi-billion-year

record of collisions; however, astronomers believe these

two icy bodies are protoplanets — the fossilized seeds of

planets that might have been. Dawn’s images of Ceres

already imply material moved from the interior onto the

surface relatively recently. Vesta is covered in craters, but

Ceres has large regions where the surface is smooth.

Its density implies a mix of rock and ice, but the world’s

exact makeup is a mystery Dawn hopes to explain. The

European Space Agency’s Herschel spacecraft found

evidence of water near the dwarf planet last year, so NASA

is eagerly seeking plumes streaming off the surface. And

strange bright spots, seen only on Ceres, might have

already delivered. In talks given at March’s Lunar and

Planetary Science Conference in Houston, Dawn scientists

said the spots might be the very ice volcanoes they’d hoped

to find, giving Dawn success upon arrival. — Eric Betz

QUICK TAKES

MOON SUPPLIES

Lunar hydrogen deposits —

possibly a sign of water — are

more abundant on south polar-

facing crater slopes, NASA’s

Lunar Reconnaissance Orbiter

found. The deposits might one

day supply water, fuel, and air.

• MAGNETIC STORMS
  NASA launched its four
  Magnetospheric Multiscale
  spacecraft in March to study
  magnetic fields connecting and
  disconnecting around Earth.
  Such explosive energy releases
  are involved in technology-
  disrupting space weather.


• 
  

  EXPLODING SUNS
  A study of planetary nebulae —
  a Sun-like star’s final stage —
  found “water fountains,”
  explosions that occur as red
  giants use up their nuclear fuel.
  It shows some suns have sur-
  prising last gasp eruptions.

  
  


• 
  

  DEEP-FRIED ICE CREAM
  Lab tests on ice and organics
  show comet surfaces get hard
  and crystalize on approach to
  the Sun as carbon-containing
  molecules are ejected — sort of
  like deep-fried ice cream.

  
  


• 
  

  NEW SPACELINER
  The European Space Agency
  launched a new spaceplane to
  advance reusable transport
  capabilities. The craft climbed
  to 75 miles (120km) and reen-
  tered the atmosphere, splash-
  ing down in the Pacific Ocean.

  
  


• 
  

  BLOCKBUSTER FIND
  Visual effects from the movie
  Interstellar led to a February
  paper in Classical and Quantum
  Gravity. The code mapped light
  beams moving through a black
  hole’s space-time, showing
  how they would be bent in
  front of a filmmaker’s camera.
  -^
  DISAPPEARING DWARF
  The Very Large Telescope’s new
  instrument, SPHERE, failed to
  find a suspected brown dwarf
  around V471 Tauri, a strange
  binary. SPHERE’s first science
  has astronomers after a new
  theory of the odd behavior.

  
  


• 
  

  FRONTIER STARS
  Brazilian astronomers found
  new star clusters at our galaxy’s
  edge — far from the inner disk
  where most form. The group
  suspects a supernova booted
  the star-forming dust and gas,
  or it was stripped as our galaxy
  skimmed a neighbor. — E. B.

  
  

TWINKLE, TWINKLE. British scientists announced plans for a small satellite named “Twinkle,” which will analyze the

atmospheres of thousands of known exoplanets, searching for spectral fingerprints of gases like water and methane.

NASA visits the

solar system’s

largest asteroid

NASA/ESA/THE HUBBLE HERITAGE TEAM (STS

CI/AURA)

CERES SUCCESS. NASA’s Dawn spacecraft reached Ceres in

March, but it approached from the far side, leaving scientists in the

dark until mid-April. NASA/JPL-CALTECH/UCLA/MPS/DLR/IDA; ASTRONOMY: ROEN KELLY

SHADOW PLAY. On January 24, the Hubble Space Telescope captured an event only seen once or twice a decade: three of Jupiter’s

moons crossing the giant planet’s face and casting their shadows on its banded surface. In the image at left, showing the beginning of

the triple-moon transit, brownish Callisto and orange-yellow Io are visible, along with their shadows and that of Europa. Some 42 min-

utes later (right image), yellow-white Europa has entered the scene at lower left, while Io no longer casts its shadow on Jupiter. — K. F.

2. 
   

million mph

(1,200 km/s)

The breakneck speed of star US 708, fast

enough to launch it out of the Milky Way.

Are these spots icy

eruptions?